The primary aim of this research is to understand the way in which lateral hypothalamic (LH) activation engendered by sexual stimuli gains access to midbrain dopamine (DA) circuitry that participates in the expression of goal-directed behaviors like sex. The experiments proposed here also seek to explain why natural reinforcers like sex, which are traditionally associated with hypothalamic circuitries, are reinforcing. One putative link between the LH and the DA system of the midbrain are hypocretin/orexin-bearing projections from the LH. Experiments detailed here will study: 1) The effect of exogenous hypocretin applied to the origin of the DA system in the ventral tegmental area (VTA) on male sex behavior; 2) The effect of activating and inactivating hypocretin signalling in the LH on forebrain DA transmission and the impact of these manipulations on male sex behavior; 3) The effect of hypocretin on unit activity in the VTA. These experiments will help to explain how the brain processes natural rewards, and findings using sex as a model for unconditionally motivated behavior may be extrapolated to other natural rewards like food or to motivational pathologies like addiction, obesity, and sexual compulsion [unreadable] [unreadable]